The hip is a ball and socket joint which has a wide range of movement. At the extremes of movement the neck of the femur comes close to or touches the elastic tissue around the rim of the socket (the labrum of the acetabulum).
If the bone of either the femur or the socket (or both) is unusually prominent then they may jam together (impinge) causing damage to the lining on the rim of the socket (a labral tear). This process may be a cause of arthritis in the hip. Impingement caused by overgrowth (a ‘bump’) on the neck of the femur is called ‘cam impingement’, whilst ‘pincer impingement’ is caused by overgrowth of the rim of the acetabulum.
Most commonly patients do not know they have impingement until some damage has occurred, and they get clicking, catching or pain in the groin. This may be a sign that the impingement has led to a labral tear. Impingement often occurs in specific positions, such as when the hip is flexed up or rotated inward. These movements are common in kicking a ball or twisting in a golf or tennis swing.
Hip impingement does not always cause problems, and many patients with bony bumps will not have pain or tears. Hip arthroscopy can be used to shave of the impinging bone, and this may improve pain and slow the progression of damage in the hip joint. It is still unclear what role impingement plays in developing arthritis and whether we can prevent arthritis by removing the impinging bone. This is an area of ongoing research.
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